LYMN^ID^E OF NORTH AMERICA. 127 



e. Shell with well-marked longitudinal folds or ribs ; geni- 

 talia and radula not recorded. 



Subgenus Polyrhytis Meek. 



EXTRALIMITAL GROUPS OF LYMN^IN^. 



Several names appear in European works which cannot be defi- 

 nitely placed in the present classification. Dr. W. Dybowski 1 has re- 

 cently instituted a subgenus Omphalobulimus for a species of Lymnsea 

 with a narrow shell, a raised and expended inner lip and a large umbili- 

 cal chink. Dybowski compares his type species (Lymncea lagorii) with 

 Lymncea vulgaris West, and also with Galba truncatula, calling atten- 

 tion to the similarity of the axis and inner lip to Limnophysa 

 (^Galba). Without an examination of the genitalia and radula it is, 

 of course, impossible to definitly postulate the correct position of this 

 group, although its affinities would appear, from the published figures 

 (which strongly resemble certain examples of palustris from New 

 York and Colorado) to be with Stagnicola. It is scarcely a form of the 

 typical Lymnseas. 



We agree with Dr. Dall, that the names proposed by Servain in 

 his Lake Balaton paper 2 are not entitled to recognition in systematic 

 nomenclature. These group names represent simply degrees of muta- 

 tion which may be found in the inhabitants of any large body of water. 

 Hazay is right in considering them physiological. Similar mutations 

 may be seen in such American species as emarginata, catascopium, 

 palustris and obrussa. 



The name Tanousia Bourguignat appears in Servain's Lake Bala- 

 ton papers and is founded on a Pleistocene fossil of Dalmatia. (Lym- 

 ncea zrmanjce Brusina). It may be thus described: "Shell small, 

 ovate, conic, closely and almost involutely coiled ; the last whorl in- 

 flated, subcarinate behind, the aperture contracted" (Dall). This 

 description recalls such Pleistocene species as Galba obrussa decampi 

 and Galba galbana, which lived in the icy waters of the Glacial Epoch. 

 According to Westerlund, this group was christened by Brusina under 

 the name of Sandria, in 1885. 



The following groups have no representatives in America, so 

 far as known : 



Zagrabica Brusina, Beitr. Pal. Oest.-Ung., 1884. — Westerlund, Acta Acad. 

 Sci. Slav. Merid., CLI, p. 119, 1902.— Dall, Alaska Mollusks, p. 65, 1905. 



^ach. Mai. Ges., XXXV, Sept. -Oct., p. 143, 1903; Bull. Acad. Imp. des Sci., 

 St. Petersb., XVIII, p. 113, 1903. — Dall, Alaska Moll., pp. 61, 63, 1905. 

 2 Hist. Mai. der Lac Balaton, 1881. 



